Interactions between eruptive activity and sector collapse at Anak Krakatau, Indonesia

Lead Research Organisation: University of Birmingham
Department Name: Sch of Geography, Earth & Env Sciences


Anak Krakatau volcano, Indonesia, collapsed catastrophically on 22nd December 2018, forming a landslide-generated tsunami that caused over 400 deaths on surrounding coastlines. Very few volcanic landslides of this size and type, known as sector collapses, have been studied in detail. Because of this, our understanding of the factors that lead to sector collapse, and therefore our capacity to forecast such events and their associated hazards, remains relatively limited. Although there have been few historical examples of large volcanic landslides, they are common on longer, geological timescales and occur across all volcanic settings. The collapse of Anak Krakatau thus provides an important opportunity to improve our knowledge of this fundamental volcanic process.

Anak Krakatau is the volcanic island that formed after the devastating eruption of Krakatau (also known as Krakatoa) in 1883, first emerging above sea level in 1929. Approximately half of the subaerial island of Anak Krakatau was removed by its recent sector collapse. The collapse occurred during an ongoing, relatively low-intensity eruption, similar to the type of activity that had characterised previous decades. However, satellite observations suggest that this style of activity changed around the time of the collapse, to a much more powerful explosive eruption. The precise timing of this change, and its potential role in the collapse, is something we will explore in detail in this research. Following the collapse, explosive activity continued and may have changed yet again, as seawater interacted with shallow erupting magma. This later stage of activity erupted large volumes of new material, rapidly filling the landslide scar and extending the island coastline in the days after the collapse.

Our research will determine the specific role of eruptive activity in the sector collapse of Anak Krakatau. We will address whether changes in eruption behaviour, involving the ascent of fresh magma, preceded the collapse and thus acted as a trigger; or whether it was the collapse itself which led to the powerful explosive eruption, by suddenly depressurising the shallow magma stored beneath the volcano. We will also define the nature of eruptive activity that took place immediately after the collapse. In this phase of the eruption, material appears to have been ejected at a very high rate, and we will test the hypothesis that the collapse destabilised the underlying magma system, leading to a change in eruption behaviour. Such processes may be common at volcanoes affected by large sector collapses, forming part of a cycle of destruction and regrowth, but are currently poorly understood.

Our work will draw upon detailed field sampling of eruption deposits spanning the collapse period. Field datasets will be interpreted alongside satellite imagery and other remote observations, numerical models that simulate eruption processes, and analyses of the chemical and textural record of magmatic processes preserved in our eruption-deposit samples. Together, our results will allow us to identify changes in the storage conditions, ascent rate and eruptive behaviour of magmas involved in different stages of activity. Our results will allow us to explore controls on the timing of the sector collapse, the role of eruptive activity in the collapse, and the impact the collapse itself had on the underlying magma system. By producing a comprehensive record of the Anak Krakatau collapse and eruptions, we will advance our understanding of volcanic sector collapses in general. We will also develop a much clearer picture of eruption processes and instabilities at Anak Krakatau, which will inform hazard mitigation plans for potential future landslides as the volcano regrows.

Planned Impact

This research will provide a comprehensive understanding of the volcanic processes involved in the sector collapse of Anak Krakatau, including the role of eruptive activity in the build up to collapse, the nature of explosive activity that accompanied the collapse, the impact of collapse on the underlying magma system, and the nature of the volcanism that led to rapid post-collapse regrowth of the island. As well as providing significant insights into eruption-associated sector collapses in general, these results have a broad importance to non-academic stakeholders including Indonesian hazard monitoring agencies and those working in the field of tsunami modelling and tsunami hazard mitigation.

Hazard monitoring agencies: Results, including technical summaries, will be shared fully with the appropriate Indonesian agencies responsible for volcanic and tsunami hazards: the Centre for Volcanology and Geological Hazard Mitigation (CVGHM), and the BMKG (the Meteorology, Climatology and Geophysical Agency, responsible for tsunami warning). We have already been in contact with relevant stakeholders to discuss our research plans, and these relationships will be developed further through pre-fieldwork meetings with these agencies. The unforeseen nature of the Anak Krakatau collapse highlights the unpredictability of sector collapses and the challenges involved in mitigating their effects. The controls on sector collapse remain poorly understood, but our detailed analysis of the event will identify the role of eruptive activity in the collapse, and will also provide a clearer understanding of post-collapse regrowth at Anak Krakatau, enabling future activity and growth to be monitored in the context of recent events. Our evaluation of a variety of remote sensing data will also help directly inform future developments of hazard monitoring at Krakatau. Collectively, our results will provide a much improved basis for forecasting future instabilities, and for developing landslide-tsunami monitoring efforts and mitigation plans on that basis.

Tsunami modellers: More generally, our results will form important additions to a comprehensive landslide-source and tsunami dataset for the Anak Krakatau event, making it the best constrained example of a large scale volcanic-island tsunami. This example can be used as a benchmark dataset against which tsunami models can be tested and improved, and then used for future landslide-tsunami hazard modelling scenarios. This is important to tsunami modellers in both academic and non-academic contexts, including those involved in coastal flood risk management and tsunami preparation in all volcanic settings, and the reinsurance sector. Results will be shared with international tsunami modelling groups (via active collaborations with S. Grilli, U. Rhode Island) and by providing a volcanological summary of the event to relevant stakeholders (e.g. to the quarterly technical meeting of the Intergovernmental Oceanographic Commission).

Wider public engagement: Our work is also likely to be of wide public interest, particularly given the effects of the Anak Krakatau collapse and its international media coverage, as well as broader awareness of Krakatau as a source of hazardous volcanic eruptions. One benefit of this type of research is increased awareness, education and engagement with scientific topics. We will distribute results through public talks, community events, museum exhibits and will also aim to publicise our research through local and national media.
Description The overall objectives of the project have been met, with the initial aim being to establish whether a shift in magmatic activity drove the collapse of Anak Krakatau, or if the reverse was true. This question is important in helping address whether monitoring data could identify precursory signals of volcanic lateral collapses. Our analysis of samples spanning the collapse demonstrates no distinctive change in the magmatic system around the event, and that the eruptive behaviour is consistent with being a response to unloading by the landslide. This is significant in terms of planning and monitoring for future events, as it implies that longer-timescale deformation processes may hold a better prospect than short term monitoring of magmatic processes in recognising incipient collapse. Ongoing research is following this up by assessment of gas outputs spanning the event, the longer-term construction of the volcano, and further collaboration to build on this investigation of collapse and tsunami hazards at island volcanoes. Our key findings have been published, providing a model of the magmatic system evolution spanning the time of lateral collapse. We are following on from this work by building further relationships with Indonesian collaborators and a planned research programme to investigate future growth and stability of Anak Krakatau, in light of our results from the 2018 event, as well as extending this research to other potentially unstable volcanic islands.
Exploitation Route The outcomes will be relevant to volcano and tsunami hazard agencies globally in terms of improving the understanding of the triggers of volcanic lateral collapses, and giving insights into what signals may precede such an event. From this and other research, improved monitoring strategies can ultimately be developed. The results will also feed into improvements in landslide tsunami modelling - the outputs of this reserach have been used to develop updated constraints on the event parameters (landslide source) that have been tested against current numerical tsunami models (in both a published research study and an updated study that is has been submitted for publication). Results have been published and shared via Indonesian partners in the project, including via public seminars. They are also feeding into future research programmes (including pending applications) to promote work that will feed into regional hazard management strategies.
Sectors Communities and Social Services/Policy


Leisure Activities

including Sports

Recreation and Tourism


Democracy and Justice


Description In addition to the previous academic outputs and collaborative work with Indonesian partners, 2023 has seen progression to the next phase of this project as a direct outcome of the initial award. In 2023, further fieldwork as conducted in collaboration with BRIN, PVMBG and ITB Indonesia, to both further explore the longer term growth and development of Anak Krakatau in the build up to its collapse, and to establish the regrowth pattern of the volcano since 2018. This has led to a co-produced DEM of the current volcano which we envisage forming part of a time-series to monitor future growth. We have used our analysis of past growth to frame this future development, in order to better forecast future potential for volcano instability. These results are due to be submitted for publication this year and we will work with BRIN and PVMBG with the aim to feed these into future hazard management strategies at Anak Krakatau. More broadly, the results of this project have been communicated widely to a public audience in both the UK and Indonesia, as well as to academic communities via journal publications and presentations, as noted in more detail above, and to hazard management agencies via Indonesian partners. In Indonesia, a series of talks given in Bandung (2019) were livestreamed to a public audience and led to a number of questions in a public discussion. A further streamed seminar was given in Bandung in 2023. The aim of the talks was to explain the aims and initial results of our research, but also to discuss the nature of lateral collapse hazards on volcanic islands, following the recent devastating impact of the Anak Krakatau collapse and tsunami. We have also reached public audiences directly in the UK through a series of outreach events (museum exhibitions, public and school group talks and informal discussions), and via media coverage of this project and broader NERC-funded reserach investigating Krakatau (e.g. media coverage on multiple news websites following the AGU conference). Further seminars were given by several members of the research team in a series of online seminars (later 2020, 2021, 2022) hosted by ITB, Indonesia, and reaching a wide university and public audience. This has strengthened ongoing collaboration with ITB, and led to the investigating team contributing to further activities via ITB and a closer collaboration. We have submitted further proposals (2022, 2023, 2024) to extend this longer-term collaborations to hazard and disaster management agencies in Indonesia, seeking to address how best to implement our results into future hazard and disaster management strategies. We will continue to disseminate our findings in Indonesia, with the longer term aim of this informing new approaches to managing volcanic island hazards in other regions characterised by partially submerged volcanoes which are prone to tsunmai hazards. This work has not only advanced our understanding of this event and the potential for lateral-collapse tsunami hazards at Anak Krakatau, but will help inform future monitoring strategies. The collaborations and insights that we've obtained through this project have also fed into current research investigating the recent explosive eruption and tsunami at Hunga Tonga-Hunga Ha'apai (funded in 2022 via a NERC Urgency Grant).
First Year Of Impact 2019
Sector Communities and Social Services/Policy,Education,Leisure Activities, including Sports, Recreation and Tourism,Government, Democracy and Justice
Impact Types Societal

Policy & public services

Description Volcanic eruption processes at Krakatau volcano, Indonesia 
Organisation Bandung Institute of Technology
Country Indonesia 
Sector Academic/University 
PI Contribution Through this project we have strengthened research collaborations with the Bandung Institute of Technology (Mirzam Abdurrachman), which has built on previous partnerships developed by a co-investigator on the project (M Cassidy). The team from Bandung offered substantial field support in Indonesia during this project, and research support (leading the drone based element of the research project), and we are continuing to work together on outputs from this project. The collaboration has also led to an upcoming research visit and is likely to support future research in the region between the two teams. We have shared data and samples resulting from the field survey, presented a series of talks in Bandung, and will continue to analyse and publish results together.
Collaborator Contribution As noted above, the partners contributed significantly to field support and led the drone-based part of the field survey; they have also contributed subsequent data and samples to the project, and the Indonesian and UK teams are continuing to work together on the project.
Impact The collaboration is not multi-disciplinary. Co-authored research publications are in preparation and will be reported here in due course.
Start Year 2019
Description Media coverage of project related research at AGU conference 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Outputs from this research project, alongside other NERC funded reserach projects investigating Krakatau (Tappin et al., eruption generated tsunamis; and Hunt et al., marine survey of Anak Krakatau) was covered widely following presentations at the AGU conference. This included articles on several international websites and a discussion on a BBC radio programme.
Year(s) Of Engagement Activity 2019
Description Multiple public talks and exhibits related to the research project (West Midlands region) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Several talks and outreach events have been given by the investigators involved in this project. Examples include an exhibit at a recent arts and science evening event (Lapworth Lates) held in the Lapworth Museum, Birmingham, where an exhibit showed samples, video and images relating to the research, as a starting point to stimulate discussions with a broad public audience. Other examples include a presentation of the reserach at the upcoming Pint of Science festival (Birmingham), and a talk to school and local interest groups at the Shropshire Geological Society.
Year(s) Of Engagement Activity 2019,2020,2021,2022
Description Seminar (hosted online by Institute of Technology, Bandung, but open to other Indonesian institutions) on tsunami hazards at island volcanoes 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact An online seminar as part of a series at Institute of Technology, Bandung, Indonesia. This will be repeated this year, and is part of an ongoing and expanding collaboration associated with this research project. These links have recently been strengthened by involvement of the PI and co-I's with ITB (for example, involvement with postgraduate students and the institution's journal), and through ongoing discussions of further collaborations with ITB and in Indonesia, not just at Anak Krakatau but more broadly into associated hazards in the region.
Year(s) Of Engagement Activity 2020,2021
Description Series of public reserach talks at Bandung Institute of Technology, Indonesia 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Following the field element of this project in Indonesia, and building on our partnership with Indonesian collaborators, four members of the reserach team presented a series of talks at Bandung Intsitute of Technology, Indonesia, about the aims of the project and initial results. The talks were given in the university but also live-streamed to a public audience. Following the talks, there was an open discussion between the speakers and the audience, including several questions from the public audience.
Year(s) Of Engagement Activity 2019